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Preliminary article... editing and pictures still
left to do!!!
As the reader you may endure my explanation or skip
to the picture and gleam your own information.
Long, long ago and far, far away, automobile use to
have something called a "generator" in them (before the widespread use
of alternators). As a child I learned from another how to use these
generators as small DC motors. This is pretty much a lost art now. As
a "wizard", I must add the educational stuff, lest you think this is all
magic.
One of the relays in the regulator on generator
system is the "cutout" relay. This relay prevents the battery current
from flowing back through the generator's armature when the generator
isn't generating. In other words, the regulator has a normally open
switch (relay) that closes when the generator is turning fast enough to
have an output voltage/current. Without this relay, when the generator
voltage drops below the battery voltage the current flows back through
the armature. The field and armature would now both be battery powered,
setting up magnetic fields. The magnetic fields produced by the field
windings and the armature are like any other magnetic poles and try to
repel each other. The armature tries to turn to align the poles but as
it rotates the commutator (brushes) change the pole positions causing
further rotation. The generator is now acting like a motor.
For this experiment I am going to connect the
generator to a lawnmower engine with a belt drive. Belt drive is the
most common arrangement for automotive generators. All the electrical
connections are the same as any basic automotive generator with one
exception - I'm adding a switch (start) to bypass the cutout relay. If
you are using this on a go-cart or an EV, this is the accelerator
switch. Close the switch and the generator starts to "motor". On my
mower engine model, the engine turns over and it starts. The engine now
turns the generator fast enough to produce the voltage to charge the
battery for the next time.
With the go-cart, letting go of the switch leaves
the inertia to spin the generator as a simple regenerative braking
system. Okay, it put something back. What it put back is not enough to
worry about. Note how fast you slowed down compared to an open circuit
(remove the Ammeter without reconnecting those wires). Free wheeling
(coasting) will probably get you further than the power put back into
the batteries will get you.
So what did we learn from all this? Well, we found
a neat way to start a small gas engine. We also learned that
regenerative braking is not (in itself) going to make electric vehicles
practical. Should I even mention that we learned a little about DC
generators and regulators.
One more note, the solenoid was added because the
current draw is too much for most pushbutton switches.
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